1. Field of the Invention
The present invention relates to a plasma processing apparatus used for processing semiconductor wafers and the like by the action of a plasma generated by microwave.
2. Description of the Background Art
In recent years, semiconductor products have been increased in density and reduced in size to a great degree. Accordingly, some manufacturing processes of the semiconductor products employ a plasma processing apparatus for such processing as film deposition, etching and ashing. In particular, there is a tendency to use a microwave plasma apparatus since the microwave plasma apparatus can produce a plasma in a stable manner even in a high-vacuum state of a relatively low pressure, specifically from about 0.1 mTorr (13.3 mPa) to several tens of mTorr (several Pa), by using the microwave or a combination of the microwave and a magnetic field from a ring-shaped coil to produce a high-density plasma.
Such a plasma processing apparatus is disclosed for example in Japanese Patent Laying-Open Nos. 3-191073 and 5-343334 and Japanese Patent Laying-Open No. 9-181052 filed by the applicant of the present application. A general plasma processing apparatus using the microwave is described briefly below in conjunction with FIGS. 6 and 7. FIG. 6 shows a structure of a conventional and generally employed plasma processing apparatus and FIG. 7 is a plan view of an insulating plate.
Referring to FIG. 6, this plasma processing apparatus 2 includes a process chamber 4 which can be evacuated, a mount base 6 on which a semiconductor wafer W is mounted, and an insulating plate 8 provided in an airtight manner on a ceiling opposite to mount base 6. Insulating plate 8 transmitting microwave is formed of aluminum nitride or the like in the shape of a disk as shown in FIG. 7, for example.
Plasma processing apparatus 2 further includes, on the upper side of insulating plate 8, a planar antenna member 10 in the shape of a disk with a thickness of several millimeters and a wave-delay member 12 formed of a dielectric for example for reducing the wavelength of microwave in the radial direction of planar antenna member 10 as required. In addition, plasma processing apparatus 2 includes a ceiling cooling jacket 16 above wave-delay member 12 that has a cooling channel 14 formed for flowing a cooling water therein in order to cool wave-delay member 12 and the like. Antenna member 10 includes a great number of microwave radiation holes 18 that are through holes nearly circular in shape. In general, microwave radiation holes 18 are arranged concentrically or spirally. An internal cable 22 of a coaxial waveguide 20 is connected to the central part of planar antenna member 10 for guiding a microwave of 2.45 GHz for example produced by a microwave generator (not shown). The microwave is transmitted radially in the radial direction of antenna member 10 and also discharged from microwave radiation holes 18 provided in antenna member 10 to be transmitted downward through insulating plate 8 into process chamber 4. The microwave generates a plasma in process chamber 4 for performing a predetermined plasma process such as etching and film deposition for a semiconductor wafer.
Insulating plate 8 demarcating the ceiling of process chamber 4 is made of aluminum nitride (AIN) for example, having in general a relatively low dielectric loss in order to transmit most of the microwave downward. Referring to FIG. 7, however, there is a tendency that a part of the microwave that is indicated by Ml is propagated radially from a central part C1 of insulating plate 8 in the radial direction thereof, reflected from the peripheral end of insulating plate 8, and accordingly returned as a reflected wave M2 to central part C1 of insulating plate 8. Consequently, reflected waves M2 concentrate at central part C1, so that the electric field of the microwave at and around central part C1 of insulating plate 8 as well as the density of accordingly produced plasma in a central region of a process space S tend to be higher than those of the surrounding regions respectively. Then, a portion of semiconductor wafer W that is located at and in the vicinity of the center thereof is plasma-processed to a greater degree than the region surrounding that portion. A resultant problem is that, in some cases, a sufficiently high planar uniformity of the plasma process is impossible to maintain.
Such a problem concerning the reflected microwave not only arises for insulating plate 8 but also similarly arises for planar antenna member 10 and wave-delay member 12, while this problem may occur to different degrees respectively. For example, the dimension of microwave radiation holes 18 of planar antenna member 10 and the pitch between the arranged holes, for example, are designed, on a calculational basis, to prevent the microwave radiated from a central part of antenna member 10 to the periphery thereof from being reflected and returned from the peripheral end of the antenna member to the central part thereof. However, because of a difference between the actual dielectric constant and a designed constant of wave-delay member 12, or for other possible reasons, at the point of time when the microwave is propagated to the outermost microwave radiation holes, all of the microwave is not radiated downward but a part thereof is reflected from the peripheral end of the antenna member and returned to the central part of the antenna member. This is inevitable and thus such a problem is desirably solved as soon as possible.
The present invention has been made in consideration of such a problem in order to effectively solve the problem. One object of the invention is to provide a plasma processing apparatus with remarkably lessened adverse effects of the reflected wave propagated in the planar direction through an insulating plate for example that seals a ceiling portion of a process chamber.
A plasma processing apparatus according to one aspect of the present invention includes a process chamber having an opened ceiling and an internal space which can be evacuated, an insulating plate airtightly attached to the ceiling of the process chamber, a mount base placed in the process chamber for mounting thereon a workpiece to be processed, a planar antenna member placed above the insulating plate and including a microwave radiation hole for transmitting therethrough microwave used for generating plasma, the microwave transmitted through the insulating plate into the process chamber, a wave-delay member placed above the planar antenna member for decreasing the wavelength of microwave, and gas supply means for supplying a predetermined gas into the process chamber. The insulating plate has its peripheral end formed into an uneven shape with depressions and protrusions for causing, reflected waves of the microwave propagated through the insulating plate from the center and in the radial direction of the insulating plate, to cancel out each other.
In the plasma processing apparatus with the structure as described above, the microwave propagated radially through the insulating plate in the process chamber is reflected from the depressions and protrusions of the peripheral end of the insulating plate, so that resultant reflected waves cancel out each other. It is thus possible to considerably lessen adverse influences of the reflected waves and accordingly improve the planar uniformity of plasma processing for the workpiece to be processed.
Preferably, the depressions and protrusions of the uneven shape each have a length in the radial direction of the insulating plate, and the length is substantially equal to an odd multiple of a quarter of the wavelength of the microwave propagated through the insulating plate.
Still preferably, a pitch, in the circumferential direction of the insulating plate, between the depressions or protrusions of the uneven shape substantially ranges from a quarter to twice as long as the wavelength of the microwave propagated through the insulating plate.
A plasma processing apparatus according to another aspect of the invention includes a process chamber having an opened ceiling and an internal space which can be evacuated, an insulating plate airtightly attached to the ceiling of the process chamber, a mount base placed in the process chamber for mounting thereon a workpiece to be processed, a planar antenna member placed above the insulating plate and including a microwave radiation hole for transmitting therethrough microwave used for generating plasma, the microwave transmitted through the insulating plate into the process chamber, a wave-delay member placed above the planar antenna member for decreasing the wavelength of microwave, and gas supply means for supplying a predetermined gas into the process chamber. The planar antenna member has its peripheral end formed into an uneven shape with depressions and protrusions for causing, reflected waves of the microwave propagated through the planar antenna member from the center and in the radial direction of the insulating plate, to cancel out each other.
In the plasma processing apparatus structured as described above, the microwave propagated radially through the planar antenna member is reflected from the depressions and protrusions of the peripheral end of the planar antenna member, so that resultant reflected waves cancel out each other. It is thus possible to considerably lessen adverse influences of the reflected waves and accordingly improve the planar uniformity of plasma processing for the workpiece to be processed.
Preferably, the depressions and protrusions of the uneven shape each have a length in the radial direction of the planar antenna member, and the length is substantially equal to an odd multiple of a quarter of the wavelength of microwave propagated through the wave-delay member.
Still preferably, a pitch, in the circumferential direction of the planar antenna member, between the depressions or protrusions of the uneven shape substantially ranges from a quarter to twice as long as the wavelength of microwave propagated through the wave-delay member.
A plasma processing apparatus according to still another aspect of the invention includes a process chamber having an opened ceiling and an internal space which can be evacuated, an insulating plate airtightly attached to the ceiling of the process chamber, a mount base placed in the process chamber for mounting thereon a workpiece to be processed, a planar antenna member placed above the insulating plate and including a microwave radiation hole for transmitting therethrough microwave used for generating plasma, the microwave transmitted through the insulating plate into the process chamber, a wave-delay member placed above the planar antenna member for decreasing the wavelength of microwave, and gas supply means for supplying a predetermined gas into the process chamber. The wave-delay member has its peripheral end formed into an uneven shape with depressions and protrusions for causing, reflected waves of microwave propagated through the wave-delay member from the center and in the radial direction of the wave-delay member, to cancel out each other.
In the plasma processing apparatus with the structure as described above, the microwave propagated radially through the wave-delay member for reducing the wavelength of microwave is reflected from the depressions and protrusions of the peripheral end of the wave-delay member, so that resultant reflected waves cancel out each other. It is thus possible to considerably lessen adverse influences of the reflected waves and accordingly improve the planar uniformity of plasma processing for the workpiece to be processed.
Preferably, the depressions and protrusions of the uneven shape each have a length in the radial direction of the wave-delay member, and the length is substantially equal to an odd multiple of a quarter of the wavelength of the microwave propagated through the wave-delay member.
Still preferably, a pitch, in the circumferential direction of the wave-delay member, between the depressions or protrusions of the uneven shape substantially ranges from a quarter to twice as long as the wavelength of the microwave propagated through the wave-delay member.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.